JP2827669B2 - Rust stabilizing steel and rust stabilizing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust-stabilized steel having a rust layer which is stable in an atmospheric corrosion environment and has excellent corrosion protection, and a rust-stabilizing method.

[0002]

2. Description of the Related Art Generally, corrosion resistance in the atmosphere can be improved by adding elements such as P, Cu, Cr, and Ni to steel. These low-alloy steels are called weather-resistant steels and self-form rust (hereinafter referred to as weather-resistant rust) that protects against corrosion in a few years outdoors.
This is a so-called maintenance-free steel that eliminates the need for anticorrosion treatment such as painting. In the weather-resistant steel, since it takes several years for weather-resistant rust having corrosion resistance to be formed on the steel material surface, floating rust or flowing rust such as red rust or yellow rust occurs during that time. However, this method has a problem that it is not only unfavorable in appearance but also causes pollution of the surrounding environment.

[0003] Regarding this problem, see, for example, Japanese Patent Application Laid-Open No. 1-1420.
No. 88 discloses that Fe ions 0.1 to 0.1
390.0 g / liter and 0.1 to 175.0 g / liter containing one or more of P, Cu, Cr, Ni, Mn ions.
A method for forming a stable protective rust on the surface of a steel material in a short period of time by forming a film by performing treatment with an acidic aqueous solution of H2.3 or less and subsequently forming a phosphate film is disclosed.

[0004]

However, in the above-mentioned prior art, the content of the treatment is complicated, for example, it is necessary to perform an appropriate pretreatment before forming the phosphate film, and the welding of the steel material is required. In such a case, it is difficult to apply treatment only to the welded portion, so that there is a problem that it is difficult to apply the method to a building structure or the like. Also, conventionally, a surface treatment method such as applying a coating film on the surface of a weather-resistant steel or applying a coating after forming a phosphate film is known, but the generation of weather-resistant rust by coating is slow. At the same time, there are also problems such as deterioration of the coating film itself and impairing the appearance. Further, when the weathering steel is so-called "barely used," it is unsightly in appearance for several years until it exhibits a beautiful dark brown color, and even if it is a weathering steel, it is placed in a specific environment. In such a case, there has been a problem that generation of the weather-resistant rust cannot be expected.

Accordingly, a main object of the present invention is to provide a process which can be carried out easily and in any place without causing any floating rust such as red rust or yellow rust or flowing rust, and in a short period of time to the atmospheric corrosion environment. An object of the present invention is to provide a method for accelerating rust stabilization for forming stable weather-resistant rust.

[0006]

The present invention SUMMARY OF] is, OH rust layer formed on the stabilizing process steel, and the steel surface rust with stable alpha-FeOOH at atmospheric corrosion environment on the steel surface ^-
And converting the rust layer into α-FeOOH by providing an environment exceeding pH 7 to provide a method for promoting rust stabilization.

The OH ^{-can be} supplied by spraying or brushing an alkaline aqueous solution such as an aqueous solution of NaOH, aqueous ammonia or KOH on the surface of the steel material.

[0008] The steel material of the present invention has a surface covered with α-FeOOH before use as a building, and a steel material already used as a building is treated with an α-FeOOH layer by the treatment method of the present invention. And both steel materials.

[0009] The rust layer formed on the surface of the steel material before the treatment is a sedimentation type film formed by corrosion involving an aqueous solution or the like. Not included. In addition, the rust layer is easily formed by outdoor exposure to the atmosphere, but by artificially placing the surface of the steel material in a dry and wet environment using various aqueous solutions, the rust layer can be quickly formed according to the frequency. Formed.

[0010]

[Action] The reason why weather-resistant rust exhibits excellent corrosion resistance as described above has been variously discussed, but conventionally, when weather-resistant steel was used as a building, several years later. The reason why floating rust such as red rust or yellow rust is not generated was considered to be due to the formation of amorphous rust on the steel material surface. However, as a result of earnest studies by the present inventors, it has been found that α-FeOOH self-formed on the surface of the steel material greatly contributes to the excellent corrosion resistance of the weatherable steel material.
Even if the weather-resistant steel is left in an atmosphere corrosive environment, after several years, the α-FeO
Although H is generated, it takes a very long time until the entire surface of the steel material is covered, and generally takes about 10 to 20 years, depending on the components of the weather-resistant steel material and the corrosive environmental conditions to be placed. It seems to be.

The present invention has been made based on the finding that the anticorrosive action of a weather-resistant steel as described above is due to α-FeOOH formed on the surface of the steel.

[0012] OH respect rust layer formed on the surface of the steel material ^-
Is supplied to form an environment having a pH of more than 7, thereby converting the α-FeOOH layer having excellent weather resistance into a stable α-FeOOH layer. In the present invention, as described above in, OH respect rust layer ^- is fed, by the environment in excess of pH 7, the Fe ions eluted from the steel quickly converted to the stable alpha-FeOOH on the environment And converts the already formed rust layer into stable α-FeOOH. The OH ^- The supply means, for example, for aqueous NaOH solution, an alkaline aqueous solution such as ammonia aqueous solution or KOH solution suffices be applied to steel surfaces, without any requiring special equipment, anywhere performed easily. If the pH at the time of the treatment exceeds 7, a stable α
-FeOOH, but especially when there is a demand for shortening the treatment time, pH 9-1.
By placing it in the environment of No. 4, rust stabilization can be further promoted. However, if emphasis is placed on improving the working environment, it is desirable to perform the treatment in a neutral environment even if the stabilization of rust is somewhat delayed. Incidentally, the steel targeted in the present invention,
Those that do not generally generate rust, such as stainless steel and Ni-based alloys, are excluded from the present invention because they do not require treatment, and mainly contain elements such as P, Cu, Cr, and Ni such as weathering steel. In addition to low-alloy steel, it also covers carbon steel.

When applying the alkaline aqueous solution,
Any method such as air spray, airless spray, or brush coating can be used. In addition, it is desirable to repeat application a plurality of times after application and then drying, from the viewpoint of generating stable rust at an early stage. However, a sufficient application effect can be expected even with one application, It is desirable to select in consideration of the surrounding corrosion environment, work efficiency, economy, etc.

Since the method of the present invention does not require special equipment and the like, and can easily carry out the rust stabilization promotion treatment, it is already used for railway vehicles, industrial machines, plant equipment, bridges, buildings and the like. It can be easily applied to weather-resistant steel and the like, and can be partially treated when cutting and welding steel materials on site.

[0015]

The effects of the present invention will be described below in detail with reference to examples. In this example, first, two types of weather-resistant steel (A) and ordinary steel (B) having the chemical components shown in Table 1 were used, and 150 mm × 60 mm × 5 mm test pieces No. 1 to 1 were used for each steel type.
No. 1 was prepared, and Nos.
7 is an aqueous ammonia solution.
A coating treatment was performed after exposure to the air outdoors for a predetermined period with an OH aqueous solution, and the test piece No. 11 was subjected to a test as a non-treatment as a comparative example. The test piece was subjected to emery paper polishing and buff polishing to give a mirror surface, and the pH value of each treatment solution was set to the value shown in Table 2.

[0016]

[Table 1]

[0017]

[Table 2]

Test pieces No. 1 to 11 subjected to the above treatment
Was exposed to the coastal area of Kitakyushu City, Fukuoka Prefecture, which is in a severely corrosive environment under the same conditions, for 70 days and 335 days, respectively, and the surface properties and the thickness reduction due to corrosion were investigated. As a result, with respect to Nos. 1 to 10 of the present invention, generation of flowing rust was hardly observed, and the color tone of the surface was uniform dark brown. In contrast, Comparative Example No.
In the test specimen No. 11, a large amount of flowing rust was generated, the color of the surface became reddish brown, and the distribution of red rust was observed in a dot-like manner. Further, as a result of investigating the components and their distribution in the rust layer by X-ray diffraction, Fourier transform infrared spectroscopy, and microlaser Raman spectroscopy, the test pieces No.
Both the 70-day exposure test specimen and the 335-day exposure test specimen had pH values.
Although the lower the value, the lower the tendency, the surface of all the test pieces was covered with uniform α-FeOOH. On the other hand, in the case of the untreated No. 11 test piece, the exposure period from the start of exposure was about 5% in 100 days.
And the range of about 15% in 365 days is the aforementioned α-
Only the area was covered with FeOOH, and the other areas were almost equally covered with β-FeOOH and γ-FeOOH. In the case of the weathering steel (A), α-FeOOH was slightly present near the steel surface, but generally it could be said that they were present in the rust layer.

Tables 3 and 4 show the results of the reduction in the thickness of each test piece for each exposure period. As is clear from Tables 3 and 4, the test pieces of Nos. 1 to 10 which are within the scope of the present invention show that both the corrosion-resistant steel (A) and the ordinary steel (B) have a reduced thickness compared to the untreated No. 11. Is suppressed to about half or less, and the effect of the rust stabilization promoting treatment of the present invention is remarkably exhibited. In comparison between the corrosion-resistant steel (A) and the ordinary steel (B), the corrosion-resistant steel (A)
Although the result is more excellent in the anticorrosion property, even with ordinary steel (B), a remarkable anticorrosion effect is apparent as compared with untreated No11.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

As is apparent from the above description, the steel treated according to the method of the present invention hardly causes floating rust such as red rust or yellow rust or flowing rust after the treatment, and has a short-term weather resistance and stable rust. Can be formed. In addition, since the treatment is easy and can be performed in a short period of time regardless of location, it is possible to produce steel covered with a stable rust layer with high anticorrosion properties at the factory stage, and to cut the steel locally. It can also be suitably used for post-processing such as welding.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-11739 (JP, A) JP-A-62-103373 (JP, A) JP-A-1-142088 (JP, A) JP-A-62 260866 (JP, A) JP-A-55-76078 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 22/00-22/86

Claims (2)

(57) [Claims] 1. A rust -stabilized steel material wherein the entire steel surface is covered with a uniform rust layer composed of α-FeOOH that is stable in an atmospheric corrosion environment. 2. An environment in which OH ^- is supplied to a rust layer formed on the surface of a steel material to have a pH of more than 7, and is made of α-FeOOH.
A method for stabilizing rust, characterized in that the rust is converted into a rust layer .